The Scientific Study of Cosmology

Cosmology is the scientific study of the large-scale properties of the universe as a whole. It endeavors the use of scientific method to understand the origin, evolution and ultimate fate of the universe. Cosmology involves the formation of theories or hypothesis about the universe which makes specific predictions for a phenomenon that can be tested with observations. The prevailing theory about the origin and evolution of our universe is “Big Bang theory”. This paper also let us know about the fate of the universe.

Foundations of Big Bang Cosmology and Geometry of the Universe

The Big Bang model is a broadly accepted theory for the evolution of the universe. The Big Bang model of Cosmology rests on two ideas: General theory of relativity and Cosmological Principle.

• General Relativity: Gravity is no longer described by a gravitational field but rather as supported to be a distortion of space-time.
• Cosmological Principle: The matter in the universe is homogeneous and isotropic.

By the assumption that the cosmological principle, it can be shown that corresponding distortion of space-time can have only three forms as shown in fig.

The geometry of Universe:

O0>1 shows positively curved like a ball

O0

O0=1 shows flat.

Matter plays a central role in Cosmology. It turns out that average density of matter uniquely determines the geometry of the universe. If the density of matter is greater than a critical density, the universe is closed. If it is less than the critical density, then the universe is open and if it is equal then the universe is flat. ( value of critical density is 6 H-atoms/m3).

Given the law of gravity and assumptions of about how matter is distributed, the next step is to work out the dynamics of the universe- how space and the matter in it evolve with time. The further information of expansion of the universe depends on the quantity of matter contained in it. Earlier space was considered to be static but it was Hubble who discovered the possibility of expansion of universe while studying distant galaxies.

Tests of Big Bang Cosmology

The Big Bang model is supported by a number of important observations.

• The expansion of the universe: It was “Sir Edwin Hubble” made an observation that galaxies were receding from us. It was the first clue for “Big Bang theory”.
• The abundance of the light element H, He, Li: The “Big Bang theory” predicts that these light elements should have been fused from proton and neutrons in the first few minutes after the “Big Bang”.
• The Cosmic Microwave Background Radiations: The Cosmic Microwave Background Radiations is the remnant heat leftover from “Big Bang”.

These three tests strongly support the “Big Bang Theory”.

Beyond Big Bang Cosmology

The “Big Bang theory” is incomplete. It fails to explain why the universe is so uniform on a large scale or nonuniform in small scale.

This is a very useful approximation to start with the basics. But we need to go beyond the Big Bang to understand the universe. We need an extension of Big Bang Theory- Inflation Theory. This refers to the explosively rapid expansion of Space-time.

The fate of the Universe

Ultimate Fate of the universe is either “Big Crunch” or “Endless expansion”. The fate of the universe is governed by the density. If the density of the universe is less than the critical density, the universe will expand forever, if the density of the universe is greater than the critical density, then gravity will win and the universe will collapse back on itself, the so-called “Big Crunch”.